Lactic acid is used as a food acidulant and flavoring and in pharmaceutical, plastics, textiles and other industrial formulations. The increased use of food and pharmaceutical products formulated with lactic acid has been primarily responsible for growth of worldwide production of lactic acid to about 300 million pounds per year which is expected to continue in the future.
Lactic acid is produced by a submerged culture fermentation process which employs molasses, potatoes or starch as feed and a microorganism, e.g., Lactobacillus del brueckii, L. bulgarcius or L. leichnanii. The fermentation product will contain carbohydrates, amino acids, proteins and salts as well as lactic acid, which must be separated from the fermentation broth.
For the separation of lactic acid, the calcium salt is precipitated. The resulting calcium lactate is filtered to remove heavy metals and some organic impurities. The regenerated lactic acid is separated from the precipitated CaSO.sub.4, e.g., by filtration, and the resulting crude lactic acid further purified by carbon treatment and sodium ferrocyanide to remove additional organic impurities and heavy metals, respectively. After filtration, the lactic acid is contacted with an ion exchange resin to remove trace ions. The purification process is complex and high purity is difficult to obtain.
European Patent No. 135,728 discloses the separation of lactic acid from a fermentation medium with an adsorbent comprising a polymer with tertiary amino groups described in U.S. Pat. No. 4,552,905. The resins are not disclosed to be in sulfate form, as applicants have herein disclosed their invention. Furthermore, the adsorbed acid is eluted with a solvent such as methanol.
U.K. Patent No. 868,926 relates to the purification and concentration of a carboxylic acid by an ion exchange mechanism using an ion exchange resin in OH.sup.-- form. After recovery of the acid by exchange with sulfurous acid, the resin is regenerated with hot water to convert the resin back to OH.sup.-- form.
U.S. Pat. No. 4,323,702 discloses the separation of carboxylic acids from a synthesis mixture with strong and weakly basic anionic exchange resins in OH.sup.-- form, using an organic solvent, e.g. alcohol, ketone or ester as a desorbent.
The invention herein can be practiced in fixed or moving adsorbent bed systems by batch or continuous processes, but the preferred system for this separation is a continuous countercurrent simulated moving bed system, such as described in Broughton U.S. Pat. No. 2,985,589, incorporated herein by reference. Cyclic advancement of the input and output streams can be accomplished by a manifolding system, which are also known, e.g., by rotary disc valves shown in U.S. Pat. Nos. 3,040,777 and 3,422,848. Flow rates in the various zones may be set and regulated by a programmed flow controller. Equipment utilizing these principles are familiar, in sizes ranging from pilot plant scale (deRosset U.S. Pat. No. 3,706,812) to commercial scale with flow rates from a few cc per hour to many thousands of gallons per hour.
The functions and properties of adsorbents and desorbents in the chromatographic separation of liquid components are well known, but for reference thereto, Zinnen et al U.S. Pat. No. 4,642,397 is incorporated herein.